This application is based on application No. 98-49911 filed in the Korean Industrial Property Office on Nov. 20, 1998, the content of which is incorporated hereinto by reference.
(a) Field of the Invention
The present invention relates to a method of preparing vinyl chloride resin, and more particularly, to a method of preparing vinyl chloride resin having excellent impact strength and processibility.
(b) Description of the Related Art
Poly(vinyl chloride), abbreviately PVC, is a commodity plastic which is widely used because of its excellent properties and resistance to other chemicals. Still more it is possible to achieve widely performance from flexible to rigid by formulating with various additives. Owing to these advantages, the PVC is used for profile, pipe, tube, electric wire, flooring material and, interior and exterior building materials and industrial use also. But as the PVC is very rigid and brittle, the final products can be easily broken and must be toughened to make it useful applications. Furthermore, the PVC resin is extruded, PVC has a large swell problem. It makes difficult to fabricate accurate products for satisfying the highly dimensional stability and precision such as thin layer or complicated shaped product. Therefore, there has been extensive work to change the weakness of the PVC-Poor impact strength and large die swell.
For improving poor impact strength of PVC, early works suggest the method of using rubbery materials having low glass transition temperature (Tg) with PVC resin formulation like as nitrile rubber or butadiene rubber, chlorinated polyethylene.
Generally, the rubber impact modifiers are prepared by graft-copolymerization with rubber particle core (prepared by emulsion polymerizing butadiene or acrylate rubber and having particle diameter 100 to 500 nm) having good impact strength an comonomer such as methylmethacrylate or styrene having good compatibility with vinyl chloride resin.
For improving the impact strength, it is very important to disperse uniformly impact modifiers previously mentioned like as core-shell structured rubber impact modifier or chlorinate polyethylene.
Chlorinated polyethylene or rubber impact modifier shows a good dispersion ability to the PVC resin, improving impact strength of PVC resin but deteriorating weatherability and transparency. Furthermore, because the rubber impact modifier is generally made by emulsion polymerization process and acquired latex coagulation method, it should be repeatedly dispersed in the vinyl chloride resin. So the rubber impact modifier""s uniform dispersion in PVC resin is generally very difficult.
For improving these disadvantages, polyolefinic (ethylene-vinyl acetate copolymer) rubber is un-situ graft copolymerized with a vinyl chloride monomer to thereby improve PVC impact resistance. However, the obtained vinyl chloride resin is difficult to fabricate into various forms.
A method for improving impact strength of vinyl chloride resin discloses U.S. Pat. No. 3,969,431. In the method, vinyl chloride or vinyl chloride mixture is suspension polymerized with one or more comonomers in the presence of butyl acrylate rubber or 2-ethylhexyl acrylate rubber impact modifier latex essentially crosslinked elastomer particles to thereby improve impact strength. However, as the impact modifier latex contains the unreacted residual emulsifier, the polymerization step is unstable and the final molded product used to show severely discoloring problem.
Alternatively, a method that a monomer with a very low glass transition temperature is copolymerized with the vinyl chloride resin, or vinyl chloride polymerization is performed by using the monomer, is disclosed in Japanese Patent Laid-open Sho. 60-255813. In this method, acrylic esters are copolymerized with vinyl chloride, or vinyl chloride is suspension polymerized in the presence of acrylic ester polymer. However, due to increases of acrylic ester contents in the polymer, formability, dynamic heat stability and flexural modulus decrease and the discoloration severely occurs.
For reducing die swell of the vinyl chloride resin, an excess amount of lubricants is added to the PVC resin formulation. However, the added lubricant has a poor compatibility to the vinyl resin, migrating to the surface of the molded product. Due to the reason, the external shape of the molded product is deteriorated and the lubricant is accumulated a mold, causing plate-put which results in product contamination and default.
It is all object of the present invention to provide a method of preparing vinyl chloride resin having a good impact strength and a lower die swell without deterioration of another properties
In order to achieve this object and others, the present invention provides a method of preparing vinyl chloride resin having a good impact strength including the 2 steps mass polymerization method. In this method, a first polymerization step is to prepare seed particle for a second polymerization step mixing a first vinyl chloride monomer with a first initiator to thereby prepare a first polymer; and adding a second vinyl chloride monomer, a second initiator and a organic siloxane polymer having the formula 1.
Alternatively, in the present invention, the organic siloxane polymer may be used in the first step rather than the second step. 
(wherein R1 is hydrocarbon having 1 to 12 carbon atoms and substituted with a group selected from the group consisting of hydrogen, alkyl, haloalkyl, aryl, haloaryl, aralkyl, polyether, fluorine, imino, epoxy and vinyl;
R2 is saturated hydrocarbon having 1 to 12 carbon atoms; and
n is an integer of 10 to 2,000)
The vinyl chloride resin of the present invention includes polymers having at least 60 weight percent of vinyl chloride monomer. The polymer includes only a vinyl chloride monomer or copolymer of the vinyl chloride monomer and other copolymerizable monomer. The copolymerizable monomer may be capable of copolymerizing with the vinyl chloride monomer and the exemplary of the monomer may be vinyl ethers; acrylates containing unsaturated double bond, epoxy or hydroxy, methacrylates; olefins such as ethylene and propylene, unsaturated aliphatic acids containing carboxylic group, such as acrylic acid, methacrylic acid, itacone acid, maleic acid and anhydride thereof.
The exemplary of the vinyl ethers may be methyl vinyl ether, ethyl vinyl ether, vinyl ether containing aliphatic compounds having carbon atoms of 12 or less. The monomer having unsaturated double bond may be ethyl acrylate, ethyl methacrylate, normal-propyl acrylate, normal-propyl methacylate, iso-propyl acrylate, iso-propyl methacrylate, secondary-butyl acrylate, secondary-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate or alphametylstyrene. Furthermore, the monomer including epoxy group may be glysidyl acrylate, glysidyl methacrylate. The monomer including carboxyl group may be acrylic acid, methacrylic acid, itaconic acid, fumaric acid or maleic acid. The monomer including hydroxy group may be 2-hydroxy ethyl acrylate, 2-hydroxy ethyl methacrylate, 2-hydroxy propyl acrylate, 2-hydroxy propyl methyacrylate, 2-hydroxy butyl acrylate or 2-hydroxy butyl methacrylate.
The present invention provides a method of preparing vinyl chloride resin. In the method, a first initiator is fed into a first polymerization reactor and the pressure is reduced. A vinyl chloride monomer is added to the reactor and the temperature increases at predetermined polymerization temperature. In this case, a first polymerization occurs. Other copolymerizable monomer may be added to the reactor.
When the conversion from monomer to polymer reaches to 10 to 12% by keeping at the increased temperature, the reactant in the first reactor is transferred to a second polymerization reactor. If the first polymerization step is performed to obtain reactant with the conversion of below 10%, vinyl chloride resin manufacturing process is unstable and it is difficult to form particles. On the contrary, if the polymerization is performed to obtain the reactant with the conversion exceeding 12%, no additional advantages is not taken.
A second vinyl chloride monomer, a second initiator and an organic siloxane polymer having formula 1 are added the second polymerization reactor. The amount of the organic siloxane polymer is 0.01 to 20 weight percent. If the amount of the siloxane polymer is below 0.01 weight percent, effects by the addition of siloxane polymer, for example, formability and impact strength improvement, do not satisfy. On the contrary, if the amount exceeds 20 weight percent, compatible of the organic siloxane polymer with vinyl chloride decreases, resulting in poor external appearance. 
(wherein R1 is hydrocarbon having 1 to 12 carbon atoms and substituted with a group selected from the group consisting of hydrogen, alkyl, haloalkyl, aryl, haloaryl, aralkyl, polyether, fluorine, imino, epoxy and vinyl;
R2 is saturated hydrocarbon having 1 to 12 carbon atoms; and
n is an integer of 10 to 2,000)
The viscosity of the organic siloxane is 20 to 100,000 Cst. If the viscosity is below the above range, extrusion property is improved, but impact strength is very slightly improved. On the contrary, the viscosity exceeds the above range, impact strength is largely improved, but extrusion property is deteriorated.
The temperature of the second polymerization reactor increases at predetermined polymerization temperature to occur a second polymerization. When the conversion from monomer to polymer reaches to 60 to 70%, unreacted vinyl chloride is removed and the polymerization terminates to thereby obtain vinyl chloride resin.
In the method, the organic siloxane polymer may be both added to the first and second reactor, or only the first reactor without addition to the second reactor.
The polymerization temperature controls polymerization degree of the vinyl chloride resin and greatly influences on the condition and characteristics of final product. Therefore, it is important to select the suitable polymerization temperature. In the present invention, the first and second polymerization are performed at the conventional polymerization temperature, for example, 30 to 80xc2x0 C.
As the initiator, organic peroxides may be used. The exemplary of the organic peroxides includes peroxides such as di-pentyperoxide, di-3,5,5,-trimethyl hexa-noylperoxide and dilauroyl peroxide; peroxicarbonates such as diisopropylperoxycarbonate, di-secondarybutylperoxydicarbonate, di-2-ethylhexylperoxycarbonate and 2-ethylhexylperoxycarbonate; peroxy ester such as t-butyl peroxy pivalate, t-butylperoxyneodecarbonate, azo compound such as azobisisobutyronitrile, azobis-2-methylbutyronitrile, azobis-2,4-dimethylvaleronitrile; sulfate such as potassium sulfate and ammonium persulfate.
The amount of the initiator depends on various manufacturing conditions such as manufacturing process, productivity and quality. The initiator amount is 0.8 to 1.5 weight percent of total monomer. If the amount is below the above range, the reaction time is longer and productivity is reduced. On the contrary, if the amount exceeds the above range, the unreacted initiator is remained in the final resin, resulting in deterioration of heat stability, color and quality of the resin.
The exemplary of the organic siloxane polymer includes at least one A: polymer or copolymer of dimethyl siloxane, methyl chlorinated phenyl siloxane, methyl hydrogen siloxane, amono-modified siloxane, epoxy modified siloxane, octamethyl cyclotetra siloxane, decamethyl cyclopenta siloxane, dodecamethyl cyclohexasilane, trimethyl triphenyl cyclotrisilane, dimetyl siloxane and 3-mercaptopropylmethyl siloxane; B: copolymer of dimetyl siloxane, vinyl dimethoxy silane; C: copolymer of 3-mercaptopropylmetyl siloxane, dimethyl siloxame and vinyl methyl dimethoxy silane; D: copolymer of dimethyl siloxane and tetra vinyl tetra methyl cyclosiloxane; and E: copolymer of organic siloxane and 30 to 80 wt % of acrylic ester.
The exemplary of acrylic ester used in the copolymer of organic siloxane and acrylic ester includes one or more methylacrylate, methylmethacrylate, ethylacrylate, ethylmethacrylate, butylacrylate, butylmethacrylate, 2-ethyl hexyl acrylate, 2-ethylhexylmethacrylate.
The obtained vinyl chloride resin of the present invention by bulk polymerizing has improved extrusion formability and impact strength.